Magnetic device and apparatus and procedure for making the same



y 1965 R. M. CLINEHENS ETAL 3,197,749

MAGNETIC DEVICE AND APPARATUS AND PROCEDURE FOR MAKING THE SAME Original Filed March 27, 1959 2 Sheets-Sheet 1 j Lil/tron! 16 20 A lA/VE/VTUAZ 5 ,icqrd lzf/kzeiena 0 174/ 4, M /'er' 0% 4 04.11 W

y 1965 R. M. CLINEHENS ETAL 3,197,749

MAGNETIC DEVICE AND APPARATUS AND PROCEDURE FOR MAKING THE SAME Original Filed March 27, 1959 2 Sheets-Sheet 2 00/74/ I Ale/er E's/i arwge;

United States Patent 3,197,749 MAGNETIC DEVICE AND APPARATUS AND PROCEDURE FOR MAKING THE SAME Richard M. Clinehens, Dayton, Ohio, and Donal A. Meier,

Inglewood, Califi, assignors to The Nationalflash Register Company, Dayton, Ohio, a corporation of Maryland Continuation of application Ser. No. 802,494, Mar. 27, 1959. This application Sept. 29, 1961, Ser. No. 143,018

7 Claims. (Cl. 340-174) This invention relates to means and methods for producing bistable magnetic coatings upon slender rod-like supports, and to the bistable magnetic devices produced thereby. Such'devices are of exceptionally small dimensions and present many outstanding advantages over the toroidal magnetic cores at present used in magnetic datastorage systems'and in magnetic switching devices.

This application is a continuation of our co-pending application Serial No. 802,494, filed March 27, 1959 and now abandoned.

The bistability characteristic of certain magnetic materials is well understood; and it is Well known that for data-storage or memory applications in computers and control devices, the B-H characteristic or loop of the magnetic material must be quite square. Squareness of the B-H characteristic is defined as the ratio of the magnetic induction at remanence to that under a particular degree of coercive force, and will herein be designated by the term 'Br/Bm. These and other characteristics of magnetic materials are explained in common texts treating the subject of electromagnetism; for example, in the text Ferromagnetism, by Bozorth.

In magnetiodata-storage devices in particular, it is desirable that the individual data-storage elements be as small as is practicable and that they be capable of changing from either remanent stateto the other within a very short interval of time while using but a very small quantity of energy. Conventional toroidal magnetic datastorage elements, or cores as they are commonly called, have been produced in very small dimensions, and are available with turnover (change of remanent state) times of the order of one microsecond. These cores are structurally delicate and require that the cooperating electrical windings be in the form of conductors which must be threaded through the opening or hole in the core. Such winding operations are tedious and time-consuming and must be performed very carefully if the cores are of small dimensions. Efforts have heretofore been made to produce other types of bistable magnetic devices usable for magnetic data-storage purposes and obviating the undesirable structural characteristics of toroidal cores. Among those ,devices proposed are electrical conductors on which is plated a relatively thick coating'of magnetic material which, when the conductor is physically subjected to twisting or torsional strain, has a magnetic orientation such that there exists an easy direction of magnetization which 'is neither longitudinal nor transverse with respect to the conductor axis but is skewed so as to extend, in a sense, spirally about the conductor; and in this strained condition, the magnetic coating possesses a degree of squareness of the 3-H loop requisite for datastorage purposes. Since the magnetic material is deposited upon an electrical conductor, relatively heavy eddy-current losses are experienced when the device is used; and for this reason the .coating of magnetic material is relatively thickand the conductors and electronic hardware used in conjunction with the device must be proportionately longer, -more expensive, etc. Further, the mentioned device requires that the plated conductors be mechanically maintained in the strained condition, which adds to the difliculties attendant upon their use as datastorage devices.

3,197,749 Patented July 2'7, 1965 Briefly, the present invention comprehends a magnetic data-storage device which is relatively free of the noted d sadvantages of the prior art magnetic data-storage devices, and includes a novel apparatus and procedure for producing the device. Basically, the data-storage device of the invention is a thin cylindrical layer of magnetic ma terial which layer is long relative to its thickness, and having desirable and requisite high Br/Bm ratio and nominal coercivity as determined with a longitudinally directed field, and preferably the layer of magnetic material being supported upon a stiff slender non-magnetic rod-like support device which is substantially free of tor.- s onal strain and which is also electrically non-conductive, whereby the magnetic material is supported relatively free of mechanical strain and is-adapted for easy insertion into and withdrawal from previously formed solenoids which constitute windings for the magnetic def vice and which windings and otherappurtenant electronic means are thus not burdened with the large eddy-current losses incurred in the mentioned coated-conductor data-storage devices and accordingly is capable of extremely rapid change of state. The support device is preferably in the form of a still slender monofilament of a non-conductive material such as glass or quartz, which is provided with a thin adherent coat of silver or other electrically conductive material so as to permit the mag: netic layer to be electroplated upon the support device. The silver coat should be of the minimum thickness consistent with satisfactory electrical conductance as a plating cathode and consistent with firm adherence to the glass or other base element. The conductive coat or substrate, and the overlying adherent layer of magnetic ma-. terial are produced in accordance with procedures which are hereinafter more fully explained and described.

One evident object of the invention is to .provide an improved magnetic device adapted for use as a-magnetic data-storage element. Another object of the-invention is to provide a magnetic data-storage element which obviates the aforementioned disadvantages of previously known magnetic data-storage elements. Another object of the invention is to provide apparatus and a procedure for making the improved magnetic elements. Other objects and advantages of the invention will hereinafter be made evident in the appended claims and description of a preferred form and mode according ,to the invention, which description includes the accompanying drawings in which: 7

FIG. 1 is a view showing in grossly magnified form, a section of a magnetic device according to the invention, with partsout of proportion to facilitate illustration and explanation; a

FIG. 2 is a drawing depicting an electron micrograph of a transverse section of a replica-representation of a portion of a magnetic device according to the invention;

FIG. 3 is a drawing representing an enlarged trans.- verse section of a part of a magnetic device according to the invention, in idealized representation, and with parts out of proportion to facilitate illustration;

FIG. 4 .isa diagrammatic representation of apparatus used to produce a silver coating or substrate upon .a rodlike base structure; r

FIG. 5 is a diagrammatic representationof apparatus used to electroplate magnetic material upon a rod-like support device; a

FIG. 6 is an end view of a magnetic devicetdisposed within a set of solenoids; and, 7

FIG. '7 is aB-H loop of a ,magnetic device according to the invention, as determined with a longitudinally applied magnetic field. 1

In FIG. 1 there is depicted somewhat diagrammatically, on a grossly enlarged scale and with relative dimena sions exaggerated, a bistable magnetic device according to the invention, a long middle portion of the device having been removed to facilitate illustration. It will be understood that the longitudinal dimension of the device may be from a few times the transverse dimension to many hundreds or thousands of times greater, as will hereinafter be made more fully evident. The magnetic device, indicated generally by the number 10, comprises a stitf-non-magnetic electrically non-conductive base structure or element 12 and very thin layers 14 and 16 of electrically conductive material and of magnetic material, respectively. The base structure 12 is preferably a single monofilament of a stiff resilient non-*nagnetic electrically non-conductive material such as glass or quartz, and serves mainly as a strain-free support for and upon which are applied other elements of the basic' magnetic device. The monofilament is of small transverse dimension, the diameter of the exemplary structure 12 hereinafter considered more in detail being about 15 mils (thousandths of an inch). The length of base element 12 is, for practical purposes, at least several times the diameter thereof, but is otherwise not critical and in some possible applications of the completed device would be hundreds of times the diameter. And while it is not necessary that the element 12 be of round cross-section, considerations relative to expense of production of the device and to operating efficiency of the final product, dictate a preference for the round configuration. The reason for stitfness in base structure 12 is to reduce or inhibit likelihood of production of physical strain in the magnetic layer 16 incident to handling of the device 10 subsequent to its manufacture.

There is illustrated in FIG. 4 an apparatus used in producing a silver substrate upon a rod-like base struc* ture 12. The apparatus is in part shown in section and with a portion broken away, to facilitate a clear explanation and illustration of the parts thereof and of their operation. A glass monofilament base structure 12a is depicted as extending between two rotary gripping devices 18 and 20 which may be rotatable pin Vises or the like. The monofilament is thus arranged and disposed for axial rotation and concurrent translation through a suitably positioned tubular guide device 22. Device 22 is provided with an opening or window 22w through which are directed jets or sprays 24s, 26s of suitable silvering solutions supplied through nozzles 24 and 26, respectively. The solutions may be any which will produce a satisfactory and very thin electrically conductive substrate upon the glass monofilament; and may for example be, respectively, Peacock Concentrated Silver Solution and Silver Spray Reducing Solution, both marketed by Peacock Laboratories, Philadelphia 34, Pennsylvania. The nozzles 24 and 26 may be of known form and are connected by tubing to respective controllable pressurized supplies (not shown) of the two solutions. The two solutions are sprayed across the region 221' through which the base structure is moved, whereby as the silver solution contacts the rotating structure 12a, it is concurrently reduced thereon by the reducer solution, leaving a very thin film or layer of silver on the surface of the glass. As an aid in obtaining a firmly adherent layer of silver, the glass rod may be and preferably is chemically cleaned (as by or with sodium dichromate solution at F. followed by water rinse) and the rod may be and preferably is sensitized by dipping in stannous chloride solution. While the electrically conductive substrate of silver may be accumulated during a single slow pass through the spray region 22r, a more uniform layer may be produced by drawing the rod through the spray quite rapidly, immediately rinsing in a distilled water spray to remove unreacted "silver salts, and repeating the procedure several times (the rod being in the meantime continuously rotated), until a satisfactory depth or thickness of silver has been produced. A silver substrate having an electrical resistance of the order of from 1.5 ohms per inch to O.4 ohm per inch is satisfactory. However, to reduce electrical losses in the final device, the silver should be a thin as will still provide satisfactory conductivity for plating and a firmly adherent magnetic layer.

The devices 18 and 29 may be moved and rotated by hand or by any suitable apparatus (not shown), it being sufiicient for the purposes of the invention that the apparatus be such as to permit a reasonable degree of uniformity in rotation and in translation of the base structure 12a through the spray zone or region 221'. Guide device 22 may be of any desired length, and is preferably such as to confine device 20 to a straight course of movement without appreciable friction.

Subsequent to the silvering process and preferably immediately thereafter, the silveracoated rod 12a is removed from devices 18 and 2t and an electrical terminal, such as 12at (FIG. 5) is applied onto the upper end portion of the silver substrate. The lower portion of the rod is then lowered into an empty tube 30 which is closed at its lower end. The upper end of the tube is then provided with a seal 32, through which seal the rod extends and is adapted to be drawn. Tube 36 and its cargo of the lower portion of rod 12a are then lowered into the relative positions indicated in FIG. 5, in a support or fixture 34 which is adapted to be disposed in an electroplating bath. The upper wing 34y of fixture 34 is provided with an upper bore 34b through which tube 30 may pass, and the lower wing 34w is provided with a smaller bore 34a through which all except an upper rim portion of the tube passes. Thus tube 30 is supported by the lower wing of the fixture, with rod 12a extending upwardly through the upper bore 3412 as shown. Fixture 34 may conveniently be made of a transparent synthetic resin or other type of electrical insulation. Disposed in a recess 34;- between the upper and lower wings of the fixture, and substantially coaxial with bores 34a and 34b, is a helical anode electrode 36, to which unidirectional electricity is supplied by way of an insulated electrical conductor 33a which is connected to a constantcurrent source 4-0 as indicated in FIG. 5. The other terminal of the source of current is connected to rod terminal 12: by means of a long flexible conductor 38b. Anode electrode 36 may be of nickel wire, and of an open-turn helical form whereby electroplating bath may freely be circulated in and through the region or zone in which electrolytic action occurs. The anode electrode may be held in place in any suitable manner, for example, by utilizing the compression-spring effect of the helical coil when the latter is compressed and then released in the position indicated. Conductor 38a may pass through sealed passages in fixture 34, as indicated.

In use, fixture 34 is disposed Within a suitable tank or container 42 which is adapted to contain the electrolyte or electroplating bath, and the fixture may be supported therein in any acceptable way, as by being suspended therein by hook bracket means 44 which is hooked over the rim of container 42 as indicated. An electrolyte 46 is introduced into container 42, to a level no more than slightly above the upper end of anode 36, as indicated. The electrolyte is a water solution of materials listed in the following table:

G./l. Ferrous chloride (FeCl .4H O) 315 Nickel chloride (NiCl .6H O) 10 Calcium chloride (CaCl Water to make solution.

The solution or electrolyte 46 is regulated to a pH of from 0.9 to 1.0, and preferably is maintained at about 75 C. Preferably also the electrolyte is maintained in a state of circulation by gentle stirring. Electric current is supplied and rod 12a is slowly raised by means 48 at such a rate that any particular point thereon is subjected to electroplating action for an appropriate time, relative to the electroplating current density, necessary to produce an iron-nickel magnetic coating or layer having acceptable magnetic characteristics. As an example, with an active electroplating zone one inch long (the distance between wings 34w and 34y) and a current density of about 31 amperes per square foot of exposed surface area of the cathode, traversal of a 'l 5-mil diameter silvered rod at the rate of one inch per 37 seconds produced on the rod a firmly adherent magnetic coating having excellent magnetic characteristics (square BH loop and optimum coercivity) for magnetic data-storage device uses. The exemplary produced magnetic layer (16) was calculated to be of an apparent average thickness in the range from 2000 A. to 3000 A. (based upon an assumed 100% plating efficiency), and was determined by chemical analysis to be composed essentially of iron and nickel in the ratio of 97 parts iron to 3 parts nickel, by weight. While variations in the time-rate of electroplating may be effected, and variations in electroplating bath used, optimum values of squareness of the BH loop are secured by following the described procedures and using the cited materials and values. A reproduction of the BH loop of the magnetic layer, as determined with a longitudinally-extending magnetic field and as displayed upon a cathode-ray oscilloscope, is shown in FIG. 7, wherefrom it may be discerned that the coercivity of the material is about 15 oersteds and the squareness (Br/Bin) of the loop is greater than 0.95.

The means for circulating the electrolyte may be thermal, mechanical, or of other suitable known type; and, being per se not of the present invention, is not illustrated in the drawings. The means for rotating and translating device 18 is similarly of any suitable conventional type and hence is not illustrated. The means 48 for traversing rod 12a through the electroplating Zone 341' is shown only diagrammatically. It may be a very light weight hoist system of slow-motion character, such as a reel, cord, and capstan driven by clockworks.

The silver substrate 14 upon which the magnetic layer 16 is electrodeposited, and the latter layer itself as well, are of such thinness as to preclude satisfactory physical examination by direct optical observation. Attempts to examine the two layers optically resulted in no provable conclusions as to presence of crystal structure or magnetic orientation. An electron-micrograph of a replica of the end of a very small portion of the silver substrate 14 and the magnetic layer 16 was produced, and a portion thereof is reproduced in FIG. 2 to indicate apparent structural characteristics and apparent thickness dimensions of the layers. The section was taken as nearly to a right-angled cross-section as was practicable. The reproduced portion of the magnified replica indicates, by the scale therebelow, the apparent relative thicknesses of the layers, the silver substrate replica being represented by Mr and the replica of the magnetic material by 16r. The left side of the reproduction of the replica of the silver represents the apparent roughness of the surface of the glass rod. The boundary intermediate 1dr and Mr represents the apparent nature of the outer surface of the silver substrate, and the right boundary of 16r indicates the apparently irregular thickness and surface configuration of the layer of magnetic material. Other electron-microscope studies of replicas of the surfaces of the silver substrate and of the magnetic layer indicate an apparently amorphous silver structure with a smooth but bumpy surface, and a definitely crystalline magnetic material structure.

The bistable magnetic device which is produced in accord with the previously explained mode or procedure and with the apparatus and environmental characteristics described, may be of any desired practical length, from a small fraction of an inch to many feet. It may be used in many obvious ways, in conjunction with electrical coils or solenoids which are used, for example, to change the remanent magnetic state, to inhibit such change, and to sense any such change. As a replacement for a series of one or more toroidal cores in magnetic data-storage devices, the device has marked advantages such as are more fully explained in copending applications of' Donal A. Meier, Serial No. 728,739,filed April 15, 1958, and now abandoned, entitled Magnetic Device, and Serial No. 796,892, filed March 3, 1959, and now Patent 3,134,965, entitled Magnetic Data-Storage Device and Matrix. An indication of the manner in which the device is employed as the magnetic data-storage element of adata-storage unit is furnished by FIG. 6, in which an end-sectional view of a device such as that denoted by 10 in- FIG I is shown encircled by appropriate coils or solenoids. In FIGS. 6, rod 12 with its layer of electrically conductive metal 14 and adherent layer 16 of magnetic material, is loosely but closely encircled by a set of five concentric solenoids 50, 51, 52, 53, and 54, from which solenoids the device 10 may be readily removed by axial movement. The solenoids, which have respective terminal ends Ella-50b, SILT-51b, etc., may be of ten turns each and of insulated wire of about #36 A.W.G. size, although the size of wire and the number of turns may be changed to suit the characteristics and requirements imposed by associated electronic equipment with which the device is to be employed. Solenoid 54 may be a sense coil in which an output potential is induced in response to change of magnetic remanent state of the device (within the solenoids), while the other solenoids may be used as half-current drive windings and inhibit windings, all as more fully indicated in the previously mentioned copending patent applications.

With this disclosure in view it will be evident that modifications of specific features thereof will occur to those skilled in the art, and accordingly it is not desired that the invention be limited to the exemplary details described other than as restricted by the appended claims.

What is claimed is:

1. A bistable magnetic device comprising: a base member of a non-magnetic material, said base member having a cylindrical surface; and a thin layer of magnetic material uniformly disposed over said surface, said magnetic material being composed of an iron-nickel alloy, substantially of 97% iron, by weight, and the remainder being nickel.

2. A bistable magnetic device comprising: a base member of a non-magnetic material, said base member having a cylindrical surface; and a thin layer of magnetic material uniformly disposed over said surface, said magnetic material being composed substantially of 97 parts iron and 3 parts nickel, by weight; the thickness of said thin layer of magnetic material being such as to provide therefor a substantially rectangular hysteresis loop.

3. A bistable magnetic device comprising: a base member of non-magnetic material, said base member having a cylindrical surface; and a thin layer of magnetic material uniformly disposed over said surface, said magnetic material being composed substantially of 97 parts iron and 3 parts nickel, by weight; the thickness of said thin layer of magnetic material being such as to provide therefor a coercivity of approximately 15 oersteds.

4. A bistable magnetic device comprising: a base member having an electrically conductive surface; and an adherent thin layer of magnetic material uniformly deposited on said surface, the thickness of said thin layer being approximately 2,000 to 3,000 angstroms and the magnetic material being composed substantially of 3 parts nickel to 97 parts iron, by weight.

5. A bistable magnetic device comprising: a thin monofilament of a non-magnetic material, a thin substrate of electrically conductive material disposed of saidmonofilament and composed substantially of silver; and a thin layer of magnetic material uniformly deposited over said substrate, said magnetic material being composed substantially of 97 parts iron and 3 parts nickel, by weight; the thickness of said thin layer being approximately 2,000 to 3,000 angstroms.

6. A bistable magnetic device comprising: a base member of a non-magnetic material having an electrically conducting surface; and an adherent thin layer of magnetic material uniformly deposited over said surface; said magnetic material being composed substantially of 97 parts iron and 3 parts nickel, by weight; the thickness of said thin layer of magnetic material being such as to provide therefore a substantially rectangular hysteresis loop.

7. A bistable magnetic device comprising: a thin monofilament of a non-magnetic material; a thin substrate of electrically conductive material uniformly disposed over said nonfilament and composed essentially of silver; and an adherent thin layer of magnetic material uniformly de posited over said substrate; said magnetic material being composed substantially of 97 parts iron and 3 parts nickel, by Weight; the thickness of said thin layer of magnetic material being such as to provide therefor a coercivity of approximately 15 oersted-s.

References Cited by the Examiner UNITED STATES PATENTS 2,792,563 5/57 Rajchman 340-474 8 2,877,540 3/59 Austen 29-155.5 2,878,463 3/59 Austen 340-174 2,906,682 9/59 Fahnoe 340-174 OTHER REFERENCES Preparation of Thin Magnetic Films, M. S. Biois, Journal of Applied Physics, vol. 26, No. 8, August 1955, pages 975-980.

A Compact Coincident-Current Memory, A. U. Pchm, S. M. Rubens, Proceedings of the Eastern Joint Computer Conference, December 10-12, 1956, pp. 120- 123.

IRVING L. SRAGOW, Primary Examiner.

WALTER W. BURNS, 111., Examiner. 

1. A BISTABLE MAGNETIC DEVICE COMPRISING: A BASE MEMBER OF A NON-MAGNETIC MATERIAL, SAID BASE MEMBER HAVING A CYLINDRICAL SURFACE; AND A THIN LAYER OF MAGNETIC MATERIAL UNIFORMLY DISPOSED OVER SAID SURFACE, SAID MAGNETIC MATERIAL BEING COMPOSED OF AN IRON-NICKEL ALLOY, SUBSTANTIALLY OF 97% IRON, BY WEIGHT, AND THE REMAINDER BEING NICKEL. 